Magnetic reed sensor suitable for use in ignition timing systems

ABSTRACT

A magnetic reed sensor comprises a generally U-shaped permanent magnet having first and second end poles defining a gap of a given distance therebetween and establishing a magnetic flux path thereacross. A reed of flexible magnetic material is fixedly mounted at one end to a support with its other end forming a cantilever projection into the magnetic flux path wherein the flux path is normally symmetrically disposed about the reed. An external ferromagnetic material moved in proximity to said symmetric flux path, creates an unbalanced flux distribution which urges the reed toward one of the pole pieces. One embodiment includes a light source and a light pipe each mounted in opposite directions from the reed so that an optical path is completed between the light source and the light pipe in response to movement of the reed. The magnetic reed sensor then serves as a light shutter which is used in conjunction with an automotive engine to provide an optical indication of the relative timing of the engine.

States atent- 1 1 1 May 28, 1974 Leonard Robin Hulls, Marblehead, Mass. 1

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Mar. 30, I973 [75] Inventor:

1211 Appl. N6; 346,670

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Primary Examiner AIfr'ed E. Smith Assistant Examiner'Rol'f Hille Olson I [57] ABSTRACT A magnetic re ed sensor comprises a generally U- shaped permanent magnet having first and second end poles defining a gap of a given distance therebetween and establishing a magnetic flux path thereacross. A reed of flexible magnetic material is fixedly mounted at one end to a support with its other end forming a cantilever projection into the magnetic flux vpath wherein the flux path is normally symmetrically disposed about the reed. An external ferromagnetic material moved in proximityto said symmetric flux path, creates an unbalanced flux distribution which urges the reed toward one of the pole pieces. One embodiment includes a light source and a light pipe each mounted in opposite directions from the reed so that an optical path is completed between the lightsource and the light pipe in response to movement of the reed. The magnetic reed sensor then serves as a light shutter which is used in conjunction with an automotive engine to provide an optical indication of the relative timing of. the engine.

I Claims, Drawing Figures Pmmmm 28 4974 saw 1 or z MAGNETIC REED SENSOR SUITABLE FOR USE IN rc vmon TIMING SYSTEMS I The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Army.

BACKGROUND OF THE INVENTION ample, the wear which occurs upon the electrical contact surfaces caused by both the physical engagement and the electrical arcing that tends to occur during the making and breaking of the electrical connection as the magnetic reed moves. Secondly,the material of the rotor device of these magnetic reed switches normally takes the form of a brittle, permanently magnetic material and is therefore not always amenable to desired rotor configurations. 1

In the present invention animproved magnetic reed sensor, which may be-utilized as a switch, is used in conjunction with a rotor which can be a soft magnetic or ferromagnetic material. One specific embodiment provides an ignition timing system utilizing the improved magnetic reed device. In this regard, prior art systems for providing ignition timing have conventionally taken the form of a portable strobe-light or stroboscope gun which is electrically coupled to the ignition system to provide a flashing light at a rate which is synchronized with engine and cylinder cycles. The strobelight thus far provided illuminates a'moving memberof the engine, which member carries a predesignated mark. Accordingly, the apparent position of the mark, in the presence of the intermittent illumination, provides a relative indication of ignition timing.

SUMMARY OF'TI-IE INVENTION Briefly, the present invention provides a magnetic reed sensor whichfacilitates, for example, ignition timing of an automotive engine. The sensor comprises a permanent magnethaving first and second end poles defining a gap of given distance therebetween and establishing a magnetic flux path thereacross. A reed of flexible magnetic material is fixedly mounted at one end to a support and has a portion of its other end disposed between the end poles in the path of the magnetic flux. Means for determining the position of the reed relative to the end poles may include a light source and a light transmission means mounted in opposite directions from the reed so that an optical path is completed between the light source and the transmission means in response to movement of the reed. In one embodiment, an ignition timing system includes a magnetic member mounted on a movable member of said engine so as to be translated through a path in close proximity to the reed, thereby, to disturb the magnetic flux path established across the poles when the moving magnetic member is in close proximity to deflect the reed. In this embodiment the light source is coupled to 2 the engine ignition system to provide pulsed output light synchronized with engine and cylinder cycles. The light transmission means of the reed sensor is extended away from the reed to provide an external viewing port. The coincidence between the completion of the optical path and the pulsed output light'provides an indication of ignition timing.

BRIEF DESCRIPTION OF THE DRAWING The advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawing wherein: I

FIGS. 1A and 1B are side elevation views of a magnetic reed sensor device, in accordance with the presentinventiomillustrating principles of, its operation;

FIGS. 2A and ZB-arecross-sectiorial elevation views of a preferred form of-the magnetic reed sensor apparatus in accordance with the invention;

FIG. 3 is a schematic diagram of an ignition timing system incorporating the magnetic reed-sensor of the present invention; and I FIGS. 4A and-4B illustrate a preferred adaptation of the system of FIG. 3 shown in conjunction with a crankshaft pulley of an automotive engine:

DETAILED DESCRIPTION OF PREF ERRED EMBODIMENTS Referring to the Figuresof the drawing, FIGS. 1A and 1B show a magnetic reedsensor apparatus 10 which includes a generally U-shaped magnet l2 having North (N) and South (S) poles. Sensor 10 includes a magneticreed 14 which is pivotally mounted about point 16. Permanent magnet 12 provides a magnetic flux path 18 which is symmetrically disposed about reed 14 when the reed is in its vertical or perpendicular position as represented in FIG. 1A. In FIG. 1A the magnetic flux exerts equal forces-on reed 14 as the flux distribution is symmetrical and accordingly the componentsof the forces at right angles to the reed are equal and opposite. The components parallel to. the reed will be in the same direction and will'result in a force tending to pull the reed vertically'downward, toward the permanent magnet. Thus, the reedis in a position of unstable magnetic equilibrium when it is located midway between the N and S poles of magnet 12.

Referring now to FIG. 1B, it can be seen that by providing, for example, a ferromagnetic member 20, in close proximity to sensor III, the magnetic lines of force 118' are no longer symmetrically disposed about reed 14. The resulting redistribution of the field creates an unbalanced moment on reed 14 which acts to move the reed toward the more concentrated magnetic flux lines about the S pole of magnet 12. If member 20 is removed from proximity to sensor 10, reed 14 will remain in a stable state in the vicinity of the S pole. However, if a fixed-restoring bias is applied to reed 14, such as for example, by fixed stops 22A and 22B, reed 14 will return to a stablecenter or vertical position upon removalof member 20.

It should now be appreciated that the movement of reed I4 is caused by disturbing the otherwise symmetric flux lines 18. It will also be appreciated that the flux lines can be disturbed by a ferromagnetic or paramagnetic material which need not be a residually magnetic material. In the context of the present specification and the appendedclaims, the term magnetic material is intended to define a material having a relative magnetic permeability greater than unity. Accordingly, the magnetic material is neither limited to a ferrous, ferromagnetic material, such as iron, nor a permanently magnetic material.

Referring now to FIGS. 2A and 28 there is shown a currently preferred embodimnt of a magnetic reed sensor adapted to provide a light shutter in accordance with the'present invention. FIG, 2A provides a side elevation of a magnetic reed sensor The sensor includes a base 30 upon which permanent magnet 12 is mounted. A housing 32 having an inner chamber 33 incapsulates sensor 10'. Housing 32, which preferably comprises a non-magnetic material such as a suitable plastic, includes through-holes 34A and 348. The magnetic reed 14, having a given width w, is fixedly mounted in an upper portion of housing 32. The setscrew 36 is used. to retain reed 14' in the upper portion of housing 32. Thus, the fixed mounting of reed 14 provides a fixed-restoring bias wherein reed 14 is normally maintained in aposition of stable equilibrium in the gap formed by the poles of magnet 12. The lower portion of reed 14 provides a shutter, ofwidth w, which may be formed by twisting the lowermost portion of reed 14' through a right angle. Housing 32 further includes setscrews 38 and 39 which provide a fixed restoring bias to reed 14. Two additional setscrews 41A and 41B are provided to act as stops which limit the travel of reed 14'.

A light source 42 is disposed in through-hole 34A and includes apair of leads 44A and 44B.which are brought out for connection to an external circuit (not shown). A light transmission means 46 is disposed in through-hole 34B and extends a given distance away from sensor 10'. Light transmission means 46 may comprise a fiber-optics bundle, a plastic light-pipe or any other suitable means for directing a source of light to a remote utilization point.

It will be appreciated by those skilled in theart that the magnetic reed sensor, in accordance with the present invention, may also be used as a magnetic reed switch. For example, setscrews 36 and 41b of FIG. 2A may be utilized as electrical terminals to provide an electrical closure when reed 14 is correspondingly deflected. Further, a suitable photo-detector can be substituted for light transmission means 46 in order to provide an electrical output signal indicative of the position of reed 14' relative to the end poles of magnet 12. Accordingly, in the latter configuration the magnetic reed sensor serves the function of a contactless magnetic switch.

Referring now to FIG. 3 there is shown a schematic representation of an ignition timing system 100, including a sensor 10' which utilizes the principles of the present invention. Ignition timing system 100 is shown coupled to breaker points 102 of an automotive engine (not shown) by way of lead 104. Lead 104' is coupled to one terminal of capacitor 106. The other terminal of capacitor 106 is coupled to a point of reference potential, schematically represented as ground, by way of a diode 108 which is serially coupled with a resistor 110. The latter terminal of capacitor 106 is also coupled to the anode of diode 112. The cathode of diode 112 is coupled to a resistor 114. Resistor 114 is coupled to light source 42 by way of lead 44A. The other terminal of light source 42, which takes the form of a light emitting diode in FIG. 3, is coupled to ground by way of lead 448. The light emitted by source 42 is schematically represented by arrows 115. The emitted light is directed toward an opaque screen 116, which corresponds to through-hole 34A of FIGS. 2A and 2B, having an aperture of a predetermined dimension. The magnetic reed sensor 10 of system includes magnetic reed 14' whose lowermost portion forms an opaque projection as discussed with reference to FIGS. 2A and 28. Finally, light transmission means 46 is extended to an external viewing point represented by an eyepiece 118.

The operation of system 100 of FIG. 3 is described as follows. As breaker points 102 open and close in synchronism with the engine and cylinder cycles, the voltage potential on lead 104 rapidly rises from ground to the full battery or ignition primary coil (not shown) potential. The current associated with the leading edge of each rising voltage pulse is conducted through diode 112, resistor 114 and light source 42. As breaker points 102 close following this rapid'rise in voltage potential, the voltage potential on lead 104 is returned to ground potential. Accordingly, a relatively negative potential, resulting from the charge stored by capacitor 106, will appear at the junction of capacitor 106 and the cathode of diode I08. Diode 108 is poled in a manner which permits the negative potential across capacitor 106 to discharge through diode 108 and serially coupled resistor 110. The purpose of resistors 110 and 114 is to provide current limiting for the discharge path and light source 42, respectively.

It will be appreciated by those skilled in the art that light source 42 may comprise any one of a number of suitable light sources. For example, light source 42 may comprise a neon lamp having its external leads appropriately coupled between the ignition secondary coil (not shown) and ground. Thus, it should now be appreciated that light source 42 provides a pulse of light of a given duration each time the ignition points open. Accordingly, each pulse of light occurs in synchronism with engine and cylinder cycles. System 100 and, more particularly, magnetic reed sensor 10 of FIG. 3 is mechanically coupled to the automotive engine in such a manner that magnetic reed 14' is caused to be deflected in synchronism with the engine and cylinder cycles. It should now be appreciated that magnetic reed 14 may be deflected by an appropriate magnetic member suitably disposed on a moving engine member, such as a crankshaft pulley. Thus, by synchronizing the deflection of magnetic reed 14 with the output light pulses provided by light source 42, a visible, external indication of ignition timing can be provided at the external termination point of light transmission means 46.

Referring now to FIGS. 4A and 48 there is shown a preferred adaptation of the system of FIG. 3 in conjunction with two views of a crankshaft pulley of an automotive engine. In FIG. 4A a crankshaft pulley 202 is shown coupled to a threaded end of crankshaft 204 and fastened thereon by a hexagonal nut 206. A magnetic member 20 is secured to pulley 202 with the same fastening means, i.e., hexagonal nut 206. Magnetic reed sensor 10' is mounted to any suitable surface or support in close proximity to a selected angular portion of pulley 202. Light transmission means 46 is extended from sensor 10' and provides an external viewing port at eyepiece 118. FIG. 413. provides a top view of pulley 202 and member 20". It should be noted that member 20' of FIGS. 4A and 4Blcan be readily formed from any suitable ferromagnetic or paramagnetic material. For example, member 20' can .be formed by appropriately working a suitable length'of conventional bar-stock. The central portion of member 20' is formed to an appropriate width so as to accommodate mounting of member 20' to crankshaft 204 by way of hexagonal nut 206. The radial extensions of member 20' may take the form of two relatively thin blades as shown in FIGS. 4A and 48. It will be observed that as pulley 202 rotates about crankshaft 204, member 20 is also caused to be translated through a predetermined path at'a rate related to the engine and cylinder cycles of the engine which imparts motion to pulley 202.

As the radial projections of member 20' pass in close proximity to magnetic reed sensor the magnetic reed 14 of sensor 10" is accordingly deflected during a corresponding portion of the crankshafts angular displacement. Thus, by preestablishing the fixed position of member with respect to rotating pulley 202, so that the light output pulses of devicelll occur in synchronism with engine and cylinder cycles, an external optical indication of engine timing can be provided by way of light transmission means 46.

It should be noted that member 20' of FIGS 4A and 4B effectively provides two'individual magnetic members spaced 180 degrees apart on crankshaft pulley 202. This is done to increase the intensity of the available light output signal. That is, in a four-cycle, fourcylinder engine, two ignition firings are experienced during each crankshaft revolution. Geometrically, these engine firings occur at points spaced 180 apart. Thus, during each crankshaft revolution, two light output pulses are provided which, therefore, may advantag'eously be utilized to increase'the available light output intensity at eyepiece 118. It should now be appreciated that by providing a dual projection with respect to member 20, the available output light is approximately twice that which would be available if a single projection were deployed; Similarly, for a four-cycle, eightcylinder engine, four radial projections may be employed to provide a maximum output light indication. However, it will be understood that, in any event, a usable output lightindication can nonethelessbe provided with but one magnetic member, i.e., a single radial projection. v

The ultimate utility of an ignition timing system such as that depicted by FIG. 3 and FIGS. 4A 4B can be realized by judiciously and advantageously aligning magnetic member 20 with reference to sensor 10. In this regard, it can be seen that the angular width of the shutter opening provided by sensor 10' may be a substantial number degress of crank angle in some system configurations. Accordingly, if the position of sensor 10' is phased with the crank angle so that the timing flash is observed only when the ignition timing is retarded, a greater degree of timing accuracy can be realized. For example, the position of sensor 10' can be selected such that the shutter just begins to open when the ignition is retarded. Thus, to realize a fixed accurate reference for the occurrence of the flash, the distributor may be adjusted tofirst produce an optical indication which indicates that the ignition timing is slightly retarded. Thereafter, the distributor can be readjusted until the flash just disappears. This, then, is the point where the flash occurs just beyond the edge of the maybe selected to correspond to the desired engine ignition timing. It will also be appreciated by those skilled in the art. that the magnetic reed shutter can be positioned in a variety of configurations in order to be utilized as an accurate indication of proper ignition timing. Further, various slits or openings can be provided at the lowermost portion of the magnetic reed l4 and- /or a corresponding slit provided at the detector end of light transmission means 46 to provide and further facilitate a desired optical signal, indicative of the desired ignition timing, at eyepiece 118.

What has been taught, then, is a magnetic reed sensor facilitating, notably, an ignition timing system. In a preferred configuration, the magnetic reed sensor provides an ignition timing device which in turn provides a means for directly observing the state of the ignition timing. Since the device in-this preferred configuration operates on the principle of coincidence. between a magnetically actuated shutter opening (driven by a magnetic member mounted on the crankshaft or other suitable moving member) and-an ignition driven flash, accurate ignition timing can be provided without necessitating an external timing device such as a strobelight or stroboscope.

What is claimed is:

1. A magnetic reed sensor ignition timing system for use with an internal combustion engine, said engine having an ignition system for producing cylinderignition at a rate synchronized with the engine and cylinder cycles of said engine,s'aid ignition timing system comprising, in combination:

a magnetic member adapted for fixed mounting to a moving member of said engine to translate said magnetic member through apredetermined cyclic translationpath and at a rate which is synchronized with the engine and cylinder cycles of said engine;

housing of non-magnetic material adapted to be fixedly mounted to a support which is disposed in close proximity to said translation path to cause said magnetic member to be in close proximity with said housing during a selected portion of. said engine and cylinder cycles;

permanent magnet mounted at one end of said housing, said magnet having first and second end poles defining a gap of given distance therebetween and establishing a magnetic flux path thereacross;

a reed of flexible magnetic material fixedly mounted at one of its ends to the other end of said housing, said reed havinga portion of its other end disposed between said end poles in said magnetic flux path wherein said reed is maintained in a state of stable equilibrium intermediate said end poles except when said magnetic member is in close proximity to said housing whereupon said magnetic flux path is disturbed causing said reed to be deflected away from said magnetic member and toward one of said end poles; and

means for determining the position of said reed relative to said cylinder ignition during said engine and cylinder cycles wherein the coincidence of a predeterminedreed position and an event indicative of said cylinder ignition during said engine and cylinder cyclesindlcates a desired ignition timing.

gine and cylinder cycles and said light transmission means providing an extension of said optical path external to said housing.

3. The system according to claim 2, wherein said light transmission means comprises a light-pipe. 

1. A magnetic reed sensor ignition timing system for use with an internal combustion engine, said engine having an ignition system for producing cylinder ignition at a rate synchronized with the engine and cylinder cycles of said engine, said ignition timing system comprising, in combination: a magnetic member adapted for fixed mounting to a moving member of said engine to translate said magnetic member through a predetermined cyclic translation path and at a rate which is synchronized with the engine and cylinder cycles of said engine; a housing of non-magnetic material adapted to be fixedly mounted to a support which is disposed in close proximity to said translation path to cause said magnetic member to be in close proximity with said housing during a selected portion of said engine and cylinder cycles; a permanent magnet mounted at one end of said housing, said magnet having first and second end poles defining a gap of given distance therebetween and establishing a magnetic flux path thereacross; a reed of flexible magnetic material fixedly mounted at one of its ends to the other end of said housing, said reed having a portion of its other end disposed between said end poles in said magnetic flux path wherein said reed is maintained in a state of stable equilibrium intermediate said end poles except when said magnetic member is in close proximity to said housing whereupon said magnetic flux path is disturbed causing said reed to be deflected away from said magnetic member and toward one of said end poles; and means for determining the position of said reed relative to said cylinder ignition during said engine and cylinder cycles wherein the coincidence of a predetermined reed position and an event indicative of said cylinder ignition during said engine and cylinder cycles indicates a desired ignition timing.
 2. The system according to claim 1, wherein said means includes a light source and light transmission means mounted in opposite directions from said reed for providing an optical path which is completed in response to the deflection of said reed, said light source being coupled to said ignition system to provide a pulsed source of output light at a rate related to said engine and cylinder cycles and said light transmission means providing an extension of said optical path external to said housing.
 3. The system according to claim 2, wherein said light transmission means comprises a light-pipe. 